Measurement and analysis by different methods of apparent radiative and conductive thermophysical properties of insulation materials

Abstract

Apparent, radiative, and conductive (true) thermal conductivity and thermal diffusivity of alumina fibre insulation materials were measured. Apparent values of both thermal diffusivity and thermal conductivity were measured on plate specimens with the use of monotonic symmetrical heating (for thermal diffusivity) and by the steady-state comparative method (for thermal conductivity). Radiative component has been calculated for each measurement from the results of theoretical studies of combined radiative-conductive heat transfer in media with multiple scattering and absorption. Optical properties of the specimen material have been measured by a special method applicable to media with strong scattering. Apparent thermal conductivity values measured directly by ASTM E 1225 steady-state plate method are significantly greater than the corresponding values derived from the measurements of apparent thermal diffusivity at temperatures higher than 900 K. This fact is explained in terms of the radiative component of heat transfer which is significantly different in the two methods.